1. Field of the Invention
The subject invention relates to a process for manufacturing colorants. More particularly, it relates to a process for manufacturing non-volatile colorants and the resulting products which are suitable for use in ribbon, ball point pen, and other inks. These colorants are manufactured from waste by-products of pararosaniline preparation.
2. Description of the Related Art
Although many of the triarylmethane dyestuffs have declined in importance in recent years, pararosaniline and its analogues have remained significant products, especially as intermediates in preparing dyes such as spirit blue, and sulfonated derivatives, for example soluble sky blue, and particularly alkali blue.
The precursors to these products have been produced by a variety of methods, for example by the condensation of substituted or unsubstituted methylenedianilines (MDA) with aniline or substituted anilines such as the toluidines. These precursors thus have the general formula: ##STR1## wherein R.sup.1 may be, by way of example, hydrogen, C.sub.1 -C.sub.8 alkyl or alkenyl, halo, cyano, or alkoxy; X.sup.- is an anion, for example an ion such as chloride, sulfate, or nitrate; and R.sub.2 is hydrogen, lower alkyl, lower alkenyl, phenyl, substituted phenyl, naphthyl, or substituted naphthyl.
The simplest member of this series is pararosaniline (paramagenta, parafuchsine, CI 42500) where R and R.sup.1 are both hydrogen. Thus the structural formula is: ##STR2## Of course, as is well known, the structural form given above represents only one cannonical version of the actual structure which is a resonance hybrid. Pararosaniline has been prepared by heating 4,4'-MDA with aniline, aniline hydrochloride, nitrobenzene, and ferric chloride; by heating aniline and p-toluidine and their hydrochlorides with iron or ferric chloride and nitrobenzene; by oxidizing a mixture of aniline and p-toluidine with arsenic acid; and by heating aniline with carbon tetrachloride and aluminum chloride. Modernly, however, the preferred method of manufacture is the air oxidation of 4,4'-MDA and aniline in excess aniline, using vanadium oxide or other suitable catalyst. Replacement of 4,4'-MDA in whole, or in part, with substituted MDAs such as 3,3'-dimethyl-4,4'-MDA or 2,2'-dimethyl-4,4'-MDA, or the replacement of aniline by substituted anilines such as the toluidines results in similar products having somewhat different color, shade, and tinctorial strength.
Following the condensation, the dyestuff is isolated in salt form, preferably as the nitrate. Excess aniline is generally removed from the filtrate by stripping in vacuo. During the removal of aniline from the filtrate, a non-volatile residue collects as bottoms in the distillation vessel. When allowed to cool, the bottoms form a hard, glassy deposit of indeterminate conposition. At regular intervals, these bottoms must be removed, preferably while still liquid, and discarded or burned. As with many other by-products of dye and pigment manufacture, disposal of such waste is expensive and problematic.